In one aspect, the invention relates to a pipe tee. In another aspect, the invention relates to improvements to a pipe tee. In yet another aspect, the invention relates to a process for forming a plastic pipe tee.
Plastic pipe has come into extensive use in recent years for handling corrosive materials, petrochemicals, and the like where metallic pipe is unsuitable; and other applications where metallic pipe is unduly expensive. The plastic pipe itself, which can be formed from a suitable thermoplastic material such as polyethylene, is usually extruded from high throughput machines.
Plastic pipe fittings for such pipes up to a pipe diameter of about 8 inches are usually injected molded. Such fittings are small and have good stress ratings and can be made economically on commercially available equipment. The larger pipe fittings, such as for pipes having a diameter from about 10 inches up to about 48 inches, are too expensive to made by injection molding since they require massive equipment and extremely high mold costs. Rotationally molded fittings can be made at considerably lower cost do to the less expensive equipment requirements. However, when pipe fittings are rotationally molded, it is extremely difficult to control the wall thickness of the fitting so as to provide sufficient strength at the areas of greatest stress. It is particularly difficult to rotationally mold large diameter pipe fittings to have long term hoop stress resistance equal to the long term hoop stress resistance of the plastic pipe to which it is to be attached. Additionally the heavy walls require extremely long cycle times and do not develop good gel on the inside surfaces. Further the heavy wall is difficult to mold without bubbles, which can lead to premature failure.
It will be extremely desirable to solve these molding problems and provide long term hoop stress resistance in the fitting equal to the long term hoop stress resistance in the piping system; to mold thinner wall pipe fittings; and to reinforce pipe fittings by economical methods.